THE INNER TISSUES OF ANIMALS. 349 



taken off, the bone yields again towards the same side when 

 again longitudinally pressed. Hence the substance of its 

 concave side, never rendered convex by a bend in the oppo- 

 site direction, would not receive any extra nutrition did no 

 other action come into play. But if we consider how inter- 

 mittent pressures must act on cartilage, we shall see that 

 there will result extra nutrition of the concave side also. 

 Squeeze between two pieces of glass a thin bit of caoutchouc 

 which has a hole through it. While the caoutchouc spreads 

 out away from the centre, it also spreads inwards, so as 

 partially to close the hole. Everywhere its molecules move 

 away in directions of least resistance; and for those near 

 the hole, the direction of least resistance is towards the hole. 

 Let this hole stand for the transverse section of one of the 

 minute canals or channels passing through cartilage, and it 

 will be manifest that on the side of the unossified bone made 

 concave in the way described, the compressed cartilage will 

 squeeze the canals traversing it; and, in the absence of 

 perfect homogeneity in the cartilage, the squeeze will cause 

 extra exudation from the canals into the cartilage. Thus 

 every additional strain will give to the cartilage it falls upon, 

 an additional supply of the materials for growth. So that 

 presently the side which, by yielding more than any other, 

 proves itself to be the weakest, will cease to be the weakest. 

 What further will happen? Some other side will yield a 

 little — the bends will take place in some other plane; and 

 the portions of cartilage on which repeated tensions and 

 pressures now fall will be strengthened. Thus the rate of 

 nutrition, greatest at the place where the bending is greatest, 

 and changing as the incidence of forces changes, will bring 

 about at every point a balance between the resistances and 

 the strains. Thus, too, there will be determined that peri- 

 pheral induration which we see in bones so circumstanced. 

 As in a shoot we saw that the woody deposit takes place 

 towards the outside of the cylinder, where, according to the 

 hypothesis, it ought to take place; so, here, we see that the 



